在C中获取/设置进程资源限制

getrlimit()和setrlimit()系统调用可用于获取和设置与进程关联的资源限制，例如文件，CPU，内存等。

Each resource has an associated soft and hard limit.

• soft limit: The soft limit is the actual limit enforced by the kernel for the corresponding resource.
• hard limit: The hard limit acts as a ceiling for the soft limit.

The soft limit ranges in between 0 and hard limit.

这两个限制由以下结构定义

struct rlimit {
    rlim_t rlim_cur;  /* Soft limit */
    rlim_t rlim_max;  /* Hard limit (ceiling for rlim_cur) */
};

系统调用的签名是

int getrlimit(int resource, struct rlimit *rlim);
int setrlimit(int resource, const struct rlimit *rlim);

资源是指您要检索或修改的资源限制。
要设置两个限制，请将具有新值的值设置为rlimit结构的元素。
要获得两个限制，请传递rlim的地址。成功调用getrlimit()会将rlimit元素设置为limit。
成功时，两者都返回0 。如果出现错误，则返回-1 ，并正确设置errno。

Here, is a program demonstrating the system calls by changing the value one greater than the maximum file descriptor number to 3.

// C program to demonstrate working of getrlimit() 
// and setlimit()
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
  
int main() {
  
    struct rlimit old_lim, lim, new_lim;
  
    // Get old limits
    if( getrlimit(RLIMIT_NOFILE, &old_lim) == 0)
        printf("Old limits -> soft limit= %ld \t"
           " hard limit= %ld \n", old_lim.rlim_cur, 
                                 old_lim.rlim_max);
    else
        fprintf(stderr, "%s\n", strerror(errno));
      
    // Set new value
    lim.rlim_cur = 3;
    lim.rlim_max = 1024;
  
    // Set limits
    if(setrlimit(RLIMIT_NOFILE, &lim) == -1)
        fprintf(stderr, "%s\n", strerror(errno));
      
    // Get new limits
    if( getrlimit(RLIMIT_NOFILE, &new_lim) == 0)
        printf("New limits -> soft limit= %ld "
         "\t hard limit= %ld \n", new_lim.rlim_cur, 
                                  new_lim.rlim_max);
    else
        fprintf(stderr, "%s\n", strerror(errno));
    return 0;
}

输出：

Old limits -> soft limit= 1048576      hard limit= 1048576 
New limits -> soft limit= 3              hard limit= 1024

旧限制值可能会因系统而异。

Now, If you try to open a new file, it will show run time error, because maximum 3 files can be opened and that are already being opened by the system(STDIN, STDOUT, STDERR).

// C program to demonstrate error when a 
// process tries to access resources beyond
// limit.
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
  
int main() {
  
    struct rlimit old_lim, lim, new_lim;
  
    // Get old limits
    if( getrlimit(RLIMIT_NOFILE, &old_lim) == 0)
        printf("Old limits -> soft limit= %ld \t"
          " hard limit= %ld \n", old_lim.rlim_cur,
                               old_lim.rlim_max);
    else
        fprintf(stderr, "%s\n", strerror(errno));
  
    // Set new value
    lim.rlim_cur = 3;
    lim.rlim_max = 1024;
  
      
    // Set limits
    if(setrlimit(RLIMIT_NOFILE, &lim) == -1)
        fprintf(stderr, "%s\n", strerror(errno));
      
    // Get new limits
    if( getrlimit(RLIMIT_NOFILE, &new_lim) == 0)
        printf("New limits -> soft limit= %ld \t"
          " hard limit= %ld \n", new_lim.rlim_cur, 
                                new_lim.rlim_max);
    else
        fprintf(stderr, "%s\n", strerror(errno));
      
    // Try to open a new file
    if(open("foo.txt", O_WRONLY | O_CREAT, 0) == -1)
        fprintf(stderr, "%s\n", strerror(errno));
    else
            printf("Opened successfully\n");
      
    return 0;
}

输出：

Old limits -> soft limit= 1048576      hard limit= 1048576
New limits -> soft limit= 3                      hard limit= 1024
Too many open files

还有另一个将两个系统调用结合在一起的系统调用prlimit()。
有关更多详细信息，请键入以下内容以查看手册

man 2 prlimit

想要从精选的最佳视频中学习和练习问题，请查看《基础知识到高级C的C基础课程》。